Such devices are used to provide stability to a body being towed e.g. by an aircraft in flight. It is known to use a rigid cone for such a purpose. However, a cone of small diameter, which is suitable for stabilizing a body being towed at high speed, is not ideally suited to low speed towing as it does not provide sufficient drag to stabilize the towed body against disturbances caused by induced oscillations propagated down the towing cable. Equally, a cone of large diameter which is suitable for the latter situation, can cause too much drag at high speed, which can place excessive strain on the towing cable.